<!DOCTYPE html>
<html>

<head>
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta charset="utf-8">
    <title>以下实例在屏幕可视窗口尺寸大于 480 像素时将菜单浮动到页面左侧：</title>
    <style>
        .wrapper {
            overflow: auto;
        }

        #main {
            margin-left: 4px;
        }

        #leftsidebar {
            float: none;
            width: auto;
        }

        #menulist {
            margin: 0;
            padding: 0;
        }

        .menuitem {
            background: #CDF0F6;
            border: 1px solid #d4d4d4;
            border-radius: 4px;
            list-style-type: none;
            margin: 4px;
            padding: 2px;
        }

        @media screen and (min-width: 480px) {
            #leftsidebar {
                width: 200px;
                float: left;
            }

            #main {
                margin-left: 216px;
            }
        }
    </style>
</head>

<body>

    <div class="wrapper">
        <div id="leftsidebar">
            <ul id="menulist">
                <li class="menuitem">Menu-item 1</li>
                <li class="menuitem">Menu-item 2</li>
                <li class="menuitem">Menu-item 3</li>
                <li class="menuitem">Menu-item 4</li>
                <li class="menuitem">Menu-item 5</li>
            </ul>
        </div>
        <div id="main">
            <h1>重置浏览器窗口查看效果！</h1>
            <p>在屏幕可视窗口尺寸大于 480 像素时将菜单浮动到页面左侧。</p>
        </div>
    </div>

</body>

</html>